Motor-driven compressors currently in use consist of a high-speed, brushless motor mounted in an aluminum housing attached to the back plate of centrifugal compressor. One current motor-driven compressor is shown in FIG. 1. As indicated in FIG. 1, the compressor wheel and casing are similar to those used in commercial internal combustion engine turbochargers. In the operation of such air compressors, the motor is energized from an external power source, such as a battery, through an electronic controller which changes the direct current from the battery to alternating current to produce a rotating magnetic field in the motor windings. The rotating field surrounding the motor magnets attached to the motor shaft generates torque that rotates the compressor wheel and shaft assembly. The compressor wheel induces air from the atmosphere or from an appropriate air cleaner and delivers it from the compressor casing at pressures above atmospheric pressure.
In current motor-driven air compressors, the amount of power produced by the motor on a continuous basis is limited by the temperature generated in the windings and by the temperature level in the electronic controller from the electrical power losses therein. Conventional low-speed motors usually employ some sort of an internal fan attached to the shaft to produce a flow of cooling air through the motor and around its internal components to limit their temperatures, however, with high-speed, brushless motors the use of internal fans become rather difficult to implement.